Far-field input in an audio system refers to an audio signal originating a far distance from the microphone(s). As examples, far-field input may be from a talker in a large room, a musician in a large hall, or a crowd in a stadium. Far-field input is contrasted by near-field input, which is an audio signal originating near the microphone(s). An example near-field input is a talker speaking into a cellular phone during a telephone call. Processing audio signals in the far field present additional challenges because the strength of an audio signal decays with the distance of the source from the microphone. The farther a person is from a microphone, the quieter the person's voice is when it reaches the microphone. Additionally, speech is reduced in clarity due to a decrease in the direct-to-reverberant ratio. Furthermore, noise sources can be present, interfering with the desired talker's voice. For example, a radio playing in the room while a person is talking makes the talker difficult to hear. When the talker is closer to the microphone than the interference source is, such as in near-field processing, the talker's voice is higher in amplitude than the interference source. When the talker is far from the microphone, such as in far-field processing, the talker's voice can be of the same or lower amplitude than the interference source. Thus, the person's voice is more difficult to discern in the presence of interference in far-field processing.
One application of far-field technology is in smart home devices. A smart home device is an electronic device configured to receive user speech input, process the speech input, and take an action based on the recognized voice command. An example smart home device in a room is shown in FIG. 1. For example, living room 100 may include a smart home device 104. The smart home device 104 may include a microphone, a speaker, and electronic components for receiving speech input. Individuals 102A and 102B may be in the room and communicating with each other or speaking to the smart home device 104. Individuals 102A and 102B may be moving around the room, moving their heads, putting their hands over their faces, or taking other actions that change how the smart home device 104 receives their voices. Also, sources of noise or interference, audio signals that are not intended to activate the smart home device 104 or that interfere with the smart home device 104's reception of speech from individuals 102A and 102B, may exist in the living room. Some sources of interference include sounds from a television 110A and a radio 110B. Other sources of interference not illustrated may include noises from washing machines, dish washers, sinks, vacuums, microwave ovens, music systems, etc.
The smart home device 104 may incorrectly process voice commands because of the interference sources. Speech from the individuals 102A and 102B may not be recognizable by the smart home device 104 because the amplitude of interference drowns out the individual's speech. In some situations, speech from a noise source, such as television 110A, may be incorrectly recognized as a speech command. For example, a commercial on the television 110A may encourage a user to “buy product X” and the smart home device 104 may process the speech and automatically order product X. Additionally, speech from the individuals 102A and 102B may be incorrectly processed. For example, user speech for “buy backpacks” may be incorrectly recognized as “buy batteries” due to interference from the interference sources.
Shortcomings mentioned here are only representative and are included simply to highlight that a need exists for improved electrical components, particularly for audio processing employed in consumer-level devices, such as audio processing for far-field pickup in smart home devices. Embodiments described herein address certain shortcomings but not necessarily each and every one described here or known in the art. Furthermore, embodiments described herein may present other benefits than, and be used in other applications than, those of the shortcomings described above. For example, similar shortcomings may be encountered in other audio devices, such as audio systems or mobile phones, and embodiments described herein may be used in mobile phones to solve such similar shortcomings as well as other shortcomings.